An antireflective film is employed in general to lower the refractive index with the use of the optical interference principle so as to prevent a decrease in contrast or image transfer caused by the reflection of outside light in image display units such as a cathode-ray tube (CTR), a plasma display panel (PDP), an electro luminescence display (ELD) and a liquid crystal display (LCD). Various attempts have been made to achieve display performance with lessened glare by, for example, forming an antiglare layer having patterned indented surface so as to scatter reflected light, or employing particles having a refractive index different from a binder so as to diffuse light inside an image display unit and enlarge the viewing angle.
Since image display units are to be used over a long time under various environments, they should be highly durable. In the case where the refractive index is lowered with the use of optical interference, there arises a problem that deterioration in the optical interference layer would cause worsening in the effect of lowering the refractive index. Moreover, nonuniform deterioration in an optical thin film results in surface irregularities thereby causing noticeable defects. Since an antireflective film is to be employed as the outermost face, it is expected that such an antireflective film also serves as a protective film of an image display unit. That is, it should be highly resistant to the sticking of dust and debris and have excellent scratch resistance.
As a protective film having excellent scratch resistance, it has been known to use a sol-gel film of hydrolytic condensation product an alkoxysilane. For example, JP-A-10-728 discloses an antireflective film of the three-layered optical interference type, JP-A-63-21601 discloses a method of lowering refractive index by forming a sol-gel film on a plastic substrate, JP-A-8-211202 discloses a sol-gel film containing an alkoxysilane and inorganic fine particles having a low refractive index, JP-A-2002-275403 discloses a sol-gel film of an organosilyl compound containing ethylenically unsaturated group, JP-A-2002-277604 discloses the combination of a sol-gel film with an antifouling layer, and JP-A-2002-265866 discloses a low refractive index coating agent comprising a fluorinated organosilane.
Although sol-gel films generally have favorable initial strength, they suffer from such problems as being fragile and frequently fouled. Moreover, they are insufficient in the durability under storage conditions with, in particular, a high humidity or wide temperature swings or in an ozone-containing atmosphere and, therefore, it has been required to overcome these problems. Although the antifouling properties can be improved by using a fluorinated organosilyl compound together, there arise some troubles in this case, for example, lowering in film strength, increase in electrostatic charge or serious sticking of dust and debris.